88 research outputs found
A COMPARISON OF THE CHARACTERISTICS AND FATE OF BARROW'S GOLDENEYE AND BUFFLEHEAD NESTS IN NEST BOXES AND NATURAL CAVITIES
Migrant Semipalmated Sandpipers (Calidris pusilla) Have Over Four Decades Steadily Shifted Towards Safer Stopover Locations
Peregrine falcons (Falco peregrinus) have undergone a steady hemisphere-wide recovery since the ban on DDT in 1973, resulting in an ongoing increase in the level of danger posed for migrant birds, such as Arctic-breeding sandpipers. We anticipate that in response migrant semipalmated sandpipers (Calidris pusilla) have adjusted migratory behavior, including a shift in stopover site usage toward locations offering greater safety from falcon predation. We assessed semipalmated sandpiper stopover usage within the Atlantic Canada Shorebird Survey dataset. Based on 3,030 surveys (totalling ~32M birds) made during southward migration, 1974â2017, at 198 stopover locations, we assessed the spatial distribution of site usage in each year (with a âpriority matching distributionâ index, PMD) in relation to the size (intertidal area) and safety (proportion of a site\u27s intertidal area further than 150 m of the shoreline) of each location. The PMD index value is >1 when usage is concentrated at dangerous locations, 1.0 when usage matches location size, and <1 when usage is concentrated at safer locations. A large majority of migrants were found at the safest sites in all years, however our analysis of the PMD demonstrated that the fraction using safer sites increased over time. In 1974, 80% of birds were found at the safest 20% of the sites, while in 2017, this had increased to 97%. A sensitivity analysis shows that the shift was made specifically toward safer (and not just larger) sites. The shift as measured by a PMD index decline cannot be accounted for by possible biases inherent in the data set. We conclude that the data support the prediction that increasing predator danger has induced a shift by southbound migrant semipalmated sandpipers to safer sites
Plumage development and molt in long-tailed manakins (chiroxiphia linearis): variation according to sex and age
Lek-mating Long-tailed Manakins (Chiroxiphia linearis) exhibit an unusual pattern of delayed plumage maturation. Each year, males progress through a series of predefinitive plumages before attaining definitive plumage in their fifth calendar year. Females also exhibit variation in plumage coloration, with some females displaying male-like plumage characteristics. Using data from mist-net captures in northwest Costa Rica (n = 1,315) and museum specimens from throughout the range of Long-tailed Manakins (n = 585), we documented the plumage sequence progression of males, explored variation in female plumage, and described the timing of molt in this species. Males progressed through a series of age-specific predefinitive plumages, which enabled the accurate aging of predefinitive-plumaged males in the field; this predefinitive plumage sequence is the basis for age-related status-signaling in these males. Females tended to acquire red coloration in the crown as they aged. However, colorful plumage in females may be a byproduct of selection on bright male plumage. Females exhibited an early peak of molt activity from February to April, little molt from May through July, and a second, more pronounced peak of molt activity in October. By contrast, males in older predefinitive-plumage stages and males in definitive plumage exhibited comparable unimodal distributions in molt activity beginning in June and peaking between July and October. Our data are consistent with selective pressure to avoid the costs of molt-breeding overlap in females and older males. Our findings have important implications for social organization and signaling in Long- tailed Manakins, and for the evolution of delayed plumage maturation in birds. Desarrollo del Plumaje y Muda en Chiroxiphia linearis: VariaciĂłn de Acuerdo al Sexo y la Eda
Delayed eggâlaying and shortened incubation duration of Arcticâbreeding shorebirds coincide with climate cooling
Biological impacts of climate change are exemplified by shifts in phenology. As the timing of breeding advances, the within- season relationships between timing of breed-ing and reproductive traits may change and cause long- term changes in the population mean value of reproductive traits. We investigated long- term changes in the timing of breeding and within- season patterns of clutch size, egg volume, incubation duration, and daily nest survival of three shorebird species between two decades. Based on previously known within- season patterns and assuming a warming trend, we hypoth-esized that the timing of clutch initiation would advance between decades and would be coupled with increases in mean clutch size, egg volume, and daily nest survival rate. We monitored 1,378 nests of western sandpipers, semipalmated sandpipers, and red- necked phalaropes at a subarctic site during 1993â1996 and 2010â2014. Sandpipers have biparental incubation, whereas phalaropes have uniparental incubation. We found an unexpected long- term cooling trend during the early part of the breeding season. Three species delayed clutch initiation by 5 days in the 2010s relative to the 1990s. Clutch size and daily nest survival showed strong within- season declines in sandpipers, but not in phalaropes. Egg volume showed strong within- season declines in one species of sandpiper, but increased in phalaropes. Despite the within- season patterns in traits and shifts in phenology, clutch size, egg volume, and daily nest sur-vival were similar between decades. In contrast, incubation duration did not show within- season variation, but decreased by 2 days in sandpipers and increased by 2 days in phalaropes. Shorebirds demonstrated variable breeding phenology and incu-bation duration in relation to climate cooling, but little change in nonphenological components of traits. Our results indicate that the breeding phenology of shorebirds is closely associated with the temperature conditions on breeding ground, the effects of which can vary among reproductive traits and among sympatric species.publishedVersio
Sex ratio varies with egg investment in the red-necked phalarope (Phalaropus lobatus)
Abstract Fisher's sex ratio theory predicts that on average parents should allocate resources equally to the production of males and females. However, when the cost/benefit ratio for producing males versus females differs, the theory predicts that parents may bias production, typically through underproduction of the sex with greater variation in fitness. We tested theoretical predictions in the red-necked phalarope, a polyandrous shorebird with sex-role reversal. Since females are larger and therefore potentially more expensive to produce and may have greater variation in reproductive success, we predicted from Fisher's hypothesis a male bias in population embryonic sex ratio, and from sex allocation theory, female biases in the clutches of females allocating more resources to reproduction. We measured eggs and chicks and sexed 535 offspring from 163 clutches laid over 6 years at two sites in Alaska. The embryonic sex ratio of 51.1 M:48.9 F did not vary from parity. Clutch sex ratio (% male) was positively correlated with clutch mean egg size, opposite to our prediction. Within clutches, however, egg size did not differ by sex. Male phalarope fitness may be more variable than previously thought, and/or differential investment in eggs may affect the within-sex fitness of males more than females. Eggs producing males were less dense than those producing females, possibly indicating they contained more yolk relative to albumen. Albumen contributes to chick structural size, while yolk supports survivorship after hatch. Sex-specific chick growth strategies may affect egg size and allocation patterns by female phalaropes and other birds
A practical and informative sandpiper monitoring procedure for the Salish Sea
The Salish Sea contains important sites for shorebirds, including migrants and winter residents. There is a need for practical, informative and easily-applied monitoring procedures and goals. Counts at stopover sites are on their own uninformative, because they are strongly affected by factors unseen by local observers. A fall in the usage of a site might signal a global population decline, but could also be due to a reduction of that siteâs quality, to an increase in site quality elsewhere such that some birds redistribute, or to changes in migratory behavior. A good framework for assessing the health of shorebird populations must encompass these alternatives. We propose a monitoring method that focusses on Pacific dunlins, the most widespread and common winter resident shorebird in the Salish Sea. The method combines a mid-winter count (Audubon Christmas Bird Count), mapping to measure the size and danger of individual sites, and a behavioral assay. Analyses of range-wide CBC counts of Pacific dunlins 1975 â 2010 give an overall demographic picture showing strong fluctuations. These data also show that the population redistributes somewhat each year, in a way that balances starvation risk and predation danger across sites. Behavioral assays give an index of how much risk shorebirds take at each site to attain requirements. We describe possible assay procedures, and how combinations of census, site attributes and measures of risk-taking at a number of sites relate to local and global changes. Our method will help ecologists and natural resource managers assess whether census changes are local, regional or global, and to diagnose the underlying causes. We also discuss how these measures might be used to measure the effectiveness of estuarine restoration projects from the shorebird point of view
Oversummering Juvenile and Adult Semipalmated Sandpipers in PerĂș Gain Enough Survival to Compensate for Foregone Breeding Opportunity
Background Age at maturity and the timing of first breeding are important life history traits. Most small shorebird species mature and breed as âyearlingsâ, but have lower reproductive success than adults. In some species, yearlings may defer northward migration and remain in non-breeding regions (âoversummeringâ) until they reach 2 years of age. Some adults also oversummer. Oversummering would be favoured by natural selection if survival were as a result raised sufficiently to compensate for the missed breeding opportunity. Several thousand Semipalmated Sandpipers (Calidris pusilla) spend the non-breeding period at Paracas, PerĂș, including individuals with long bills (likely from eastern Arctic breeding populations ~ 8000 km distant) and short bills (likely from western Arctic breeding populations, up to 11,000 km distant), with short-billed birds more likely to oversummer. We tested the prediction that oversummering birds have higher survival than migrants, and that the magnitude of this higher survival for oversummering birds is enough to compensate for their lost breeding season.
Methods We used a Multi-State Mark-Recapture model based on 5 years of encounter data (n = 1963 marked birds, and 3229 resightings) obtained year-round at Paracas, PerĂș, to estimate seasonal (i.e. breeding and non-breeding) survivorship for migrant and oversummering birds. We calculated the magnitude of the oversummering survival advantage required to compensate, for both yearlings and adults, based on published measures of annual survival and reproductive success. Using bill length as a proxy for migration distance, we investigated whether migratory survival is distance-dependent.
Results We estimate that 28% of yearlings and 19% of adults oversummer. Survival is higher for oversummering birds than for migrants, and the oversummering survival advantage is greater for adults (0.215) than for yearlings (0.140). The theoretical thresholds predicted by the size of the missed reproductive opportunity are 0.240 for adults and 0.134 for yearlings. Migratory survival decreases and the oversummering rate increases with migration distance, as assessed by culmen length.
Conclusions Our results support the life history hypothesis that oversummering raises survival enough to compensate for the loss of a breeding opportunity. Greater migration distance lowers survival and increases the probability of oversummering
Predictors of invertebrate biomass and rate of advancement of invertebrate phenology across eight sites in the North American Arctic
Average annual temperatures in the Arctic increased by 2â3 °C during the second half of the twentieth century. Because
shorebirds initiate northward migration to Arctic nesting sites based on cues at distant wintering grounds, climate-driven
changes in the phenology of Arctic invertebrates may lead to a mismatch between the nutritional demands of shorebirds
and the invertebrate prey essential for egg formation and subsequent chick survival. To explore the environmental drivers
afecting invertebrate availability, we modeled the biomass of invertebrates captured in modifed Malaise-pitfall traps over
three summers at eight Arctic Shorebird Demographics Network sites as a function of accumulated degree-days and other
weather variables. To assess climate-driven changes in invertebrate phenology, we used data from the nearest long-term
weather stations to hindcast invertebrate availability over 63 summers, 1950â2012. Our results confrmed the importance
of both accumulated and daily temperatures as predictors of invertebrate availability while also showing that wind speed
negatively afected invertebrate availability at the majority of sites. Additionally, our results suggest that seasonal prey avail ability for Arctic shorebirds is occurring earlier and that the potential for trophic mismatch is greatest at the northernmost
sites, where hindcast invertebrate phenology advanced by approximately 1â2.5 days per decade. Phenological mismatch
could have long-term population-level efects on shorebird species that are unable to adjust their breeding schedules to the
increasingly earlier invertebrate phenologies.publishedVersio
Development of intraspecific size variation in black coucals, whiteâbrowed coucals and ruffs from hatching to fledging
Most studies on sexual size dimorphism address proximate and functional questions related to adults, but sexual size dimorphism usually develops during ontogeny and developmental trajectories of sexual size dimorphism are poorly understood. We studied three bird species with variation in adult sexual size dimorphism: black coucals (females 69% heavier than males), whiteâbrowed coucals (females 13% heavier than males) and ruffs (males 70% heavier than females). Using a flexible Bayesian generalized additive model framework (GAMM), we examined when and how sexual size dimorphism developed in body mass, tarsus length and bill length from hatching until fledging. In ruffs, we additionally examined the development of intrasexual size variation among three morphs (Independents, Satellites and Faeders), which creates another level of variation in adult size of males and females. We found that 27â100% of the adult interâ and intrasexual size variation developed until fledging although none of the species completed growth during the observational period. In general, the larger sex/morph grew more quickly and reached its maximal absolute growth rate later than the smaller sex/morph. However, when the daily increase in body mass was modelled as a proportion, growth patterns were synchronized between and within sexes. Growth broadly followed sigmoidal asymptotic models, however only with the flexible GAMM approach, residual distributions were homogeneous over the entire observation periods. These results provide a platform for future studies to relate variation in growth to selective pressures and proximate mechanisms in these three species, and they highlight the advantage of using a flexible model approach for examining growth variation during ontogeny
The rate of telomere loss is related to maximum lifespan in birds
Telomeres are highly conserved regions of DNA that protect the ends of linear chromosomes. The loss of telomeres can signal an irreversible change to a cell's state, including cellular senescence. Senescent cells no longer divide and can damage nearby healthy cells, thus potentially placing them at the crossroads of cancer and ageing. While the epidemiology, cellular and molecular biology of telomeres are well studied, a newer field exploring telomere biology in the context of ecology and evolution is just emerging. With work to date focusing on how telomere shortening relates to individual mortality, less is known about how telomeres relate to ageing rates across species. Here, we investigated telomere length in cross-sectional samples from 19 bird species to determine how rates of telomere loss relate to interspecific variation in maximum lifespan. We found that bird species with longer lifespans lose fewer telomeric repeats each year compared with species with shorter lifespans. In addition, phylogenetic analysis revealed that the rate of telomere loss is evolutionarily conserved within bird families. This suggests that the physiological causes of telomere shortening, or the ability to maintain telomeres, are features that may be responsible for, or co-evolved with, different lifespans observed across species.This article is part of the theme issue 'Understanding diversity in telomere dynamics'
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